1. Field of the invention
The present invention generally relates to a light controlling sheet in use for the optical indicators, and more particularly, to a light controlling sheet for permitting only the substantially parallel light to pass therethrough.
2. Description of background art
Conventionally, the light controlling sheet of a type, as described above has been utilized as an indication face member for covering a front face of, for example, a switch mounted on an instrument panel of a motor vehicle. In the switch with the light controlling sheet as described above, a light source i.e. a lamp, is arranged in the switch housing. When the lamp is illuminated at night, the light passes through the light controlling sheet toward a driver so that the driver can visually recognize the position of the switch.
Referring to FIG. 1, a typical type of light controlling sheet C is illustrated which comprises a louver element 2. A transparent base film 4 is generally cemented to the rear surface of the louver element 2. The louver element 2 includes a plurality of walls 2a which are arranged parallel to each other on the transparent base film 4 and which may be formed in arbitrary patterns, such as honeycomb, stripe and grid patterns. The louver element 2 is so opaque that the light striking thereto can be absorbed therein. When the above light controlling sheet C is applied to an optical indicator, for example a front face of a switch mounted on an instrument panel of a motor vehicle, a light source (not shown) is arranged behind the transparent base film 4. The oblique light L.sub.1 and L.sub.2 emitted from the light source strikes the surface of the walls 2a of the louver element 2 to be absorbed therein. In the meanwhile, the substantially parallel light L.sub.0 can pass through the base film 4 and the spaces between the adjacent walls 2a. Thus, only the substantially parallel light reaches the eyes of the observer. In addition, in the above construction, the base film 4 can be removed when the walls 2a are connected to each other.
In the meanwhile, the walls 2a of the louver element 2 are opaque or dark, as described above, in order to absorb the incident light. Therefore, when the light controlling sheet C is not illuminated by a lamp as the light source during the daytime, the indication face comprising the light controlling sheet is not attractive. Therefore, the observer can not easily recognize the position of the indication face such as a front indication face of the switch.